The effects of different boron (B) dosages (0, 2 and 12 mg B/kg) were determined on four soybean (Glycine max (L.) Merr.) cultivars, namely 13935, Türksoy, ME 3399 and Deficiency. B contents of the dried plant samples, dry weight, total oil, biomass, seed yield (g/pot), seed protein contents and seed fatty acid compositions were estimated. The seed protein content and shoot dry weight of soybean cultivars increased and decreased with B supply, respectively. The seed oil of cv. Türksoy had the highest ratio of stearic and oleic acids under 2 mg B/kg treatment. The highest total oil content under 12 mg B/kg treatment was observed in cv. Deficiency with 8% higher total oil content. The ratio of saturated fatty acids to unsaturated fatty acids decreased in cvs. 13935 and ME 3399, and increased in cvs. Türksoy and Deficiency at B treatments. Seeds oil of cvs. 13935 and ME 3399 showed the highest α-linolenic acid levels under 2 mg B/kg and 12 mg B/kg soil treatment, respectively. The study revealed that high concentrations of boron had a diminishing effect on seed yield (except cv. Türksoy), increasing effect on protein content and variable effect on saturated and unsaturated fatty acid compositions. This specifies the involvement of boron in the formation of seed protein and fatty acids in soybean. However, detailed research is required to understand the mechanisms behind the process.